A known regulator and shut-off valve for a corrosive media, particularly for a wet chlorine containing gas and a chloride ion containing fluid, comprises a pressure resistant housing and a shut-off member held between at least two seat rings. The housing has a passage for the corrosive media. The seat rings are supported in he housing and contact the shut-off member under stress.
Regulating and shut-off valves to which my invention can be applied include all currently marketed structural variations for these valves. It is particularly applicable to a ball valve, a wedge-shaped gate valve, a flat slider gate valve and a stopcock valve. The valve can be a single passage valve with a single entrance and outlet or also a multiple path valve such as a three way valve.
The material for the housing is selected to suit the media fed through the valve so that on the one hand the housing is corrosion resistant and on the outer hand the housing has sufficient abrasion and erosion resistance because of the higher flow speed and turbulence.
A plurality of steel alloys and a plurality of special materials are available for the housing material. Sometimes, particularly for a processing plant in the chemical industry, the properties of the available materials are not sufficient. Either the corrosion resistance of the material is not satisfactory or the material is not suitable for the housing of the valve because it has unsatisfactory mechanical properties, particularly a reduced wear resistance or a low bending and flexure moment or torque resistance.
A significant problem is the selection of a suitable material for a valve which could be used in a plant in which a wet chlorine containing gas and/or a chloride ion containing fluid is being processed.
That also is true for a plant in which boiling solutions of alkalai, alkaline earth and heavy metal salts are processed as well as organic acids. Of course it is known that titanium has a good corrosion resistance to these media; however titanium is very soft and is unsatisfactory by itself as a housing material because of insufficient wear resistance. That is also true when the material at the surface is hardened by a TiN layer. The layer thickness attained by known layering techniques is much too small and is worn away in operation much too quickly. These layers are not renewable either.